Method and device for etching patterns inside objects

ABSTRACT

Systems and methods for etching complex patterns on an interior surface of a hollow object are disclosed. A method generally includes positioning a laser system within the hollow object with a focal point of the laser focused on the interior surface, and operating the laser system to form the complex pattern on the interior surface. Motion of the laser system and the hollow object is controlled by a motion control system configured to provide rotation and/or translation about a longitudinal axis of one or both of the hollow object and the laser system based on the complex pattern, and change a positional relationship between a reflector and a focusing lens of the laser system to accommodate a change in distance between the reflector and the interior surface of the hollow object.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.15/457,313, filed Mar. 13, 2017, which claims the benefit under 35U.S.C. § 119(e) of prior U.S. provisional application Ser. No.62/306,954, filed Mar. 11, 2016, the entire disclosures of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to methods and devices for generatingetched patterns on an interior surface of a hollow object, includingobjects with restricted access or space limited openings.

BACKGROUND OF THE INVENTION

Etching processes such as chemical etching and electrochemical etchingcan be used to carve into the exteriors of ferrous alloy or other metalobjects which are not easily engraved by other means. Etching, sometimesreferred to as milling, uses corrosive chemicals or electric current toengrave patterns into a substrate. Generally, a masking material orcoating is applied to the substrate and removed from areas that are tobe etched. The substrate may then be exposed to an etchant to form adesired pattern in the substrate.

In chemical etching processes, the coatings are resistant to thecorrosive properties of a chemical etchant. For electrochemical etching,or EChE, the coating is electrically non-conductive, and is thusresistant to ablation of the substrate surface by an electric current.For example, in an EChE process, an electric circuit is established witha suitable cathode fixed at a desired distance from the substrate, whichacts as the anode. An electrolyte compatible with both anode and cathodematerials is introduced between the cathode and anode, and then currentis passed through the circuit. Metal ions from the exposed portions ofthe substrate are dissolved or dislocated into the electrolyte at a rateproportional to the current applied.

In all etching methods, the coating needs to be removed from thesubstrate in the desired pattern so that exposure to the etchant mayremove a portion of the substrate. For non-uniformly shaped objects,such as an exterior of a three dimensional object, this may not be astraight-forward process. Furthermore, removing the coating in a patternhas generally not been possible on interior surfaces of certain objectssuch as hollow objects due to the lack of appropriate tools andprocesses. That is, no technology for scribing and etching the internalsurfaces of hollow, three-dimensional objects or shapes composed offerrous alloy or other substrate is readily available.

SUMMARY OF THE INVENTION

The presently disclosed invention provides methods and devices foretching patterns onto the interior surface of a hollow object. Themethods and devices are adaptable for use in the hollow interior of anyshaped object and may be used to create any style of pattern, whether tofacilitate a particular use for the finished object or to achieve aparticular interior aesthetic.

Accordingly, the present invention includes a laser machining apparatusfor machining an inner surface of a hollow object. Machining may includeremoval or deposition of materials such as laser ablation, lasercutting, laser welding, etc. The apparatus comprises a laser sourceconfigured to output a collimated laser beam; a focusing lens forfocusing the laser beam to provide a focal length (f); a reflector forchanging a direction of the laser beam; and an adjustment mechanism forchanging a distance (A) between the focusing lens and the reflector,wherein the adjustment mechanism allows a distance (B) between thereflector and a work piece to be varied without changing the focallength (f) of the laser beam.

According to certain aspects of the presently disclosed laser machiningapparatus, the adjustment mechanism may comprise an inner tube havingthe focusing lens mounted therein, and an outer tube having thereflector mounted therein, wherein the inner tube is configured to movewithin the outer tube to change the distance (A).

According to certain aspects of the presently disclosed laser machiningapparatus, the inner tube may comprise a collimator at a proximal endand the focusing lens at a distal end, and the outer tube may comprisethe reflector at a distal end, wherein the inner tube is nested withinthe outer tube so that the focusing lens is proximal to the reflector,and the inner tube is configured for linear motion within the outertube. The linear motion may be actuated by a ball screw controlled by aservo motor, which may be in electronic communication with a server. Theserver may be configured to receive dimensional data of an internalshape of the hollow object, and to control the servo motor based on thedimensional data.

According to certain aspects of the presently disclosed laser machiningapparatus, the apparatus may further comprise a position sensing deviceconfigured to measure the distance (B) between the reflector and thework piece, wherein the adjustment mechanism (e.g., the servo motor) isconfigured to change the distance (A) between the focusing lens and thereflector based on the distance (B) measured by the position sensingdevice.

The present invention further includes a system for patterning an innersurface of a hollow object. The system comprises a mounting stageconfigured to securely mount the hollow object and provide rotationalmovement about a longitudinal axis of the hollow object; and any of thelaser machining or mechanical scribing devices as detailed herein,wherein the scribing or machining devices are configured to fit withinan interior of the hollow object. A path of the one or more scribingblades of the scribing device or the laser of the laser machining devicein any direction (i.e., x, y, or z of a coordinate axis); rotationaland/or longitudinal movement of the hollow object; rotational and/orlongitudinal movement of the mounting stage; or any combination thereof,may be controlled manually or by an automated controller.

The present invention also includes a method for generating a patterneddesign onto an inner surface of a hollow object. The method comprisesapplying to the inner surface of the hollow object a layer of coatingwhich resists corrosive chemical etchants; removing a portion of thecoating from the inner surface in the patterned design; etching theinner surface of the hollow object in the patterned design; andstripping a remaining portion of the coating from the inner surface ofthe hollow object to reveal the patterned design.

The present invention also includes an additional method for generatinga patterned design onto an inner surface of a hollow object. The methodcomprises applying to the inner surface of the hollow object a layer ofcoating which acts as an electrical insulator; removing a portion of thecoating from the inner surface in the patterned design;electrochemically etching the inner surface of the hollow object in thepatterned design; and stripping a remaining portion of the coating fromthe inner surface of the hollow object to reveal the patterned design

According to certain aspects of the presently disclosed methods,removing the portion of the coating in the patterned design is bymechanical scribing, laser ablation, photoresist imaging and developingor a combination thereof In cases where the coating is a photoresist,removing the portion of the coating in the patterned design is by lasertreatment of the photoresist, which may be followed by developing andhardening steps to remove the treated photoresist and harden theuntreated photoresist, or vice versa, depending on the type ofphotoresist. The photoresist material may be resistant to chemicaletchants and/or an electrical insulator.

According to certain aspects of the presently disclosed methods, etchingthe inner surface in the patterned design is by applying a corrosiveagent which chemically mills the patterned design in the inner surface,or by electrochemical etching which uses electric current to mill thepatterned design. According to certain aspects of the presentlydisclosed methods, etching the inner surface in the patterned design isby laser ablation or vaporization of the material of the inner surfacein the pattered design.

The present invention also relates to methods for forming an etchedpattern on an interior surface of a hollow object. According to certainaspects, the method comprises positioning a laser system within a hollowobject so that a focal point of the laser system is focused on aninterior surface of the hollow object; operating the laser system toform a complex pattern on the interior surface of the hollow object,wherein motion of one or both of the laser system and the hollow objectis controlled by a motion control system so that the laser system formsthe complex pattern on the interior surface of the hollow object; andchanging a positional relationship between a reflector of the lasersystem and a focusing lens of the laser system to accommodate a changein a distance between the reflector and the interior surface of thehollow object so that the focal point remains focused on the interiorsurface, wherein the change in the distance between the reflector andthe interior surface of the hollow object is caused by a non-uniformshape of the interior surface. The motion control system may beconfigured to provide rotation about the longitudinal axis andtranslation along the longitudinal axis for one or both of the hollowobject and the laser system based on the complex pattern.

According to certain aspects of the presently disclosed methods forforming an etched pattern, the adjustment provided by the motion controlsystem may be inversely proportional to the distance between thereflector of the laser system and the interior surface of the hollowobject. Moreover, the adjustment may be based on real-time dimensionaldata of the distance between the reflector and the interior surface ofthe hollow object collected by a position sensing device attached to thelaser system. The adjustment may be based on dimensional data of aninterior shape of the hollow object stored on a server.

The present invention also relates to methods for forming an etchedpattern on an interior surface of a hollow object. According to certainaspects, the method comprises positioning a laser system within a hollowobject so that a focal point of the laser system is focused on aninterior surface of the hollow object; and operating the laser system tomachine a complex pattern on the interior surface of the hollow object.According to certain aspects, the machining may comprise deposition ofmaterial or ablation of material. Motion of the laser system and thehollow object may be controlled by a motion control system configuredto: provide rotation about a longitudinal axis and translation along thelongitudinal axis for one or both of the hollow object and the lasersystem based on the complex pattern; and change a positionalrelationship between a reflector of the laser system and a focusing lensof the laser system to accommodate a change in a distance between thereflector and the interior surface of the hollow object so that thefocal point of the laser system remains focused on the interior surface.The change in the positional relationship between the reflector and thefocusing lens is based on real-time dimensional data of the distancebetween the reflector and the interior surface of the hollow objectcollected by a position sensing device attached to the laser system, orbased on dimensional data of an internal shape of the hollow objectstored on a server.

According to certain aspects of the presently disclosed methods forforming an etched pattern, the laser system may include an inner tubecomprising the focusing lens at a distal end and a collimator at aproximal end, and an outer tube comprising the reflector at a distalend, wherein the inner tube is nested within the outer tube with thefocusing lens proximal to the reflector, and wherein changing thepositional relationship between the reflector and the focusing lens ismoving the distal end of the inner tube closer to the distal end of theouter tube such as, for example, by actuation of a ball screw controlledby a motor.

The present invention also relates to methods for forming a complexpattern on an interior surface of a hollow object having a smallopening. According to certain aspects, the method comprises passing alaser system through the small opening of the hollow object so that afocal point of the laser system is focused on the interior surface ofthe hollow object. The laser system generally comprises a reflector toangle the focal point with respect to a longitudinal axis of the lasersystem onto the interior surface of the hollow object, such as by anangle of about 30° to 150°, or about 45° to 135°, or about 60° to 120°,or about 75° to 105°, or about 90°. the method further comprisesproviding rotational and translational movement along a longitudinalaxis for one or both of the hollow object and the laser system based onthe complex pattern, and operating the laser system to form the complexpattern on the interior surface of the hollow object, wherein formingthe complex pattern comprises deposition of material or ablation ofmaterial in the complex pattern. The method further comprises changing alongitudinal distance between the reflector of the laser system and afocusing lens of the laser system to accommodate a change in a lateraldistance between the reflector and the interior surface of the hollowobject so that the focal point remains focused on the interior surface,wherein the change in the distance is caused by a non-uniform shape ofthe interior surface of the hollow object, and wherein a diameter of thesmall opening of the hollow object is 90%, 80%, 70%, 60%, 50%, 40%, 30%,20%, 10% or less than an interior diameter of the hollow object.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects, features, benefits and advantages of the embodiments hereinwill be apparent with regard to the following description, appendedclaims, and accompanying drawings. In the following figures, likenumerals represent like features in the various views. It is to be notedthat features and components in these drawings, illustrating the viewsof embodiments of the presently disclosed invention, unless stated to beotherwise, are not necessarily drawn to scale.

FIG. 1A illustrates a side perspective view of a mechanical scribingdevice in an engaged position in accordance with certain aspects of thepresently disclosed invention;

FIG. 1B illustrates an opposite side perspective view of the mechanicalscribing device shown in FIG. 1A;

FIG. 1C illustrates a top view of the mechanical scribing device shownin FIG. 1A;

FIG. 1D illustrates a side view of the mechanical scribing device shownin FIG. 1A in a retracted position

FIGS. 2A-2E illustrate various stages of a process for use of a laserscribing device in accordance with certain aspects of the presentlydisclosed invention;

FIGS. 3A and 3B illustrate close-up views of the laser scribing deviceshown in FIGS. 2B and 2C, respectively;

FIGS. 4A and 4B illustrate various stages of a process for use of adevice for deposition of a chemical etchant agent on an interior surfaceof a hollow object in accordance with certain aspects of the presentlydisclosed invention;

FIGS. 5A-5E illustrate various stages of a process for use of a devicefor deposition of a coating, or stripping agent on an interior surfaceof a hollow object in accordance with certain aspects of the presentlydisclosed invention;

FIG. 6A illustrates a system for scribing an inner surface of a hollowobject in accordance with certain aspects of the present invention,wherein a scribing device of the system is not yet engaged within theinner surface of the hollow object;

FIG. 6B illustrates the system shown in FIG. 6A, wherein the scribingdevice is engaged within the inner surface of the hollow object;

FIG. 7 illustrates the basic principles of focal length and depth offocus for an exemplary laser beam;

FIGS. 8A-8C illustrate various stages of entry of a laser machiningdevice into a hollow object in accordance with certain aspects of thepresently disclosed invention;

FIGS. 9A-9C illustrates adjustment of a laser machining device of thepresently disclosed invention to accommodate variations in distancebetween the device and a substrate; and

FIG. 10 is a block diagram of a system for scribing or machiningaccording to certain aspects of the presently disclosed invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, the present invention is set forth in thecontext of various alternative embodiments and implementations involvingmethods and devices for etching patterns on an inner surface of a hollowobject. Such etching methods generally employ the use of a mechanicalblade(s), a laser, or photoresist imaging and developing processes tocut, image, or scribe patterns into protective coatings on the innersurface of a hollow object, such as a hollow metal object, thus exposingthe underlying material. The coating and pattern forming processes maybe followed by the application of agents which chemically orelectrically dissolve the material which is exposed in the scribedpattern. Alternatively, material may be built up in the scribed patternon the inner surface. While the following description discloses numerousexemplary embodiments, the scope of the present patent application isnot limited to the disclosed embodiments, but also encompassescombinations of the disclosed embodiments, as well as modifications tothe disclosed embodiments.

Various aspects of the device may be illustrated by describingcomponents that are coupled, attached, and/or joined together. As usedherein, the terms “coupled”, “attached”, and/or “joined” areinterchangeably used to indicate either a direct connection between twocomponents or, where appropriate, an indirect connection to one anotherthrough intervening or intermediate components. In contrast, when acomponent is referred to as being “directly coupled”, “directlyattached”, and/or “directly joined” to another component, there are nointervening elements shown in said examples.

Various aspects of the method and device may be described andillustrated with reference to one or more exemplary implementations. Asused herein, the term “exemplary” means “serving as an example,instance, or illustration,” and should not necessarily be construed aspreferred or advantageous over other variations of the devices, systems,or methods disclosed herein. “Optional” or “optionally” means that thesubsequently described event or circumstance may or may not occur, andthat the description includes instances where the event occurs andinstances where it does not. In addition, the word “comprising” as usedherein means “including, but not limited to”.

Relative terms such as “lower” or “bottom” and “upper” or “top” may beused herein to describe one element's relationship to another elementillustrated in the drawings. It will be understood that relative termsare intended to encompass different orientations of aspects of thedevice in addition to the orientation depicted in the drawings. By wayof example, if aspects of the device in the drawings are turned over,elements described as being on the “bottom” side of the other elementswould then be oriented on the “top” side of the other elements as shownin the relevant drawing. The term “bottom” can therefore encompass bothan orientation of “bottom” and “top” depending on the particularorientation of the drawing.

It must also be noted that as used herein and in the appended claims,the singular forms “a”, “an”, and “the” include the plural referenceunless the context clearly dictates otherwise. Unless defined otherwise,all technical and scientific terms used herein have the same meanings ascommonly understood by one of ordinary skill in the art.

Terms such as “substantially parallel” or “substantially perpendicular”may be taken to indicate an angle that is within 20° of the recitedangle. Thus, substantially perpendicular, for example, may be taken tomean an angle of 90°±20°, such as 90°±10°, or even 90°±5°.

The term “etch” may be used herein to indicate that a pattern may beformed on a surface of a substrate, wherein the pattern may includeremoval or deposition of material. According to certain aspects of thepresently disclosed methods and systems, removal of the material fromthe surface of the substrate may include use of a chemical etchant,electrochemical etchant, vaporization or ablation of material using alaser, or any combination thereof.

The presently disclosed invention includes methods for etching patternsinside a hollow object. The method may comprise the following sequence:i) Surface preparation such as object pre-cleaning, and coating theinterior (and if necessary, exterior) of the object; ii) Patterngeneration by one of a) mechanical or manual scribing and peeling, b)laser ablation, or c) photoresist coating and laser (or other lightsource) exposure, development and hardening; iii) Etching by eitherchemical or electrical methods; and iv) Finishing the etched object,wherein finishing may include coating removal, surface passivation,and/or protectant application. The various steps in the method arefurther detailed below.

i) Surface Preparation and Coating

Objects to be etched by methods and devices of the present inventioninclude an internal hollow region accessible through at least oneopening, such as the inner surface of a cylinder or container. Theobjects may be formed of any durable material known in the art, such asglass, metal, metal alloys, silicon containing materials, and/or durablepolymers. For example, the objects may be formed of transition metalsand post-transition metals such as iron, gold, silver, platinum, nickel,ruthenium, palladium, molybdenum, chromium, copper, tantalum, titanium,tungsten, zinc, aluminum, indium, tin, gallium, lead, and alloys ofthese metals such as steel, brass, bronze, gallium arsenide, and indiumtin oxide. Furthermore, the objects may be formed of more than onematerial. For example, the objects may include different materialsforming the inner and outer surfaces thereof.

The objects may include a protective layer (“protectant”) which preventsdamage or oxidation during storage and/or transport. For example,protectants commonly used to prevent metal corrosion during shipment maybe composed of oil, grease, polymer films or other oxide films. Theseprotectants may chemically interfere with etching or interior coatingadhesion. Consequently, these protectants may be chemically ormechanically removed prior to coating. Typical chemical removal involveseither dissolving the protectant in a compatible solvent solution, orreacting the protectant with a suitable chemical followed by rinsing, aswith commercial detergent solutions. Protectants may also bemechanically removed by surface grit-blasting and/or high pressurerinsing.

In order to prevent unwanted etching and oxidation on the outsidesurfaces of the object, the object exterior may be dipped in, rolled, orsprayed with, a selected coating that is resistant to the selectedetchant. Depending on the solids content of the selected coating,multiple applications may be necessary, allowing for sufficient dryingtime between applications. The coatings used are generally customized toprotect the object from the selected etchant while avoiding any harm tothe underlying material of the object.

Several methods facilitate internal object coating. One exemplary methodis spraying the selected coating into the hollow interior of the objectwhile the object is fixed on a support platform, such as a rotatingapparatus. A spray head may be mounted on an extension tool allowinginsertion into openings that are too restrictive for a spray gun itselfto be inserted. The coating may be applied by inserting the spray gun(or spray head on the extension) into the object, initiating objectrotation, activating the spray, and withdrawing the spray gun (or sprayhead on the extension). The spray may be deactivated as the spray heador gun exits the object. The object may continue to rotate until thecoating dries to the point that it will no longer run or sag. Thisprocess may be manual or automated using a programmable controller.

Coating thickness may be adjusted by altering the speed at which thespray gun (or spray head) is withdrawn, and/or changing the parametersof the spray gun (e.g., spray pressures, spray tip orifice, and coatingviscosity). The rotation speed may be varied to achieve uniform coatingdistribution and thickness. The extraction speed, spray parameters androtational speed are generally determined based on the particularcoating characteristics and object dimensions.

Alternatively, internal coating of the object may be achieved by pouringthe selected coating into the hollow interior of the object while theobject is fixed on the rotating apparatus. The object may be rotated ata speed sufficient to permit uniform coating distribution and thickness.Numerous layers of coating may be applied to the hollow interior of theobject, depending on the desired coating thickness and the coatingproperties. Furthermore, depending on the viscosity of the coating anddiameter of the object, the rotational speed may require furtheroptimization, with thicker coatings requiring slower rotational speedsthan thinner coatings, and larger diameter objects requiring slowerrotational speeds than smaller diameter objects.

Another method for internal coating of container-like objects is tocompletely fill the hollow interior with the selected coating, followedby removal of excess coating. The selected coating may be removed, forexample, by placing the hollowed object upside down, thus allowing theexcess coating to drain from the hollow interior through the opening.The coating thickness may be influenced by changing the coatingviscosity and the amount of time it is allowed to remain in the hollowinterior of the object. Several repetitions of this process may benecessary to build the desired coating thickness.

After each application, the coating may be allowed to cure in a mannerwhich prevents damage to the preceding application, and/or which doesnot inhibit future applications. The term “cure”, as used in connectionwith a cured coating, means that at least a portion of the componentsthat form the coating are polymerized, cross-linked, or dried to form ahardened film. Curing or drying reactions to form the hardened film maybe carried out under ambient conditions, or may be carried out atelevated temperatures, pressures, or in the presence of various gases.For example, the coating may comprise a solvent which may be evaporatedto dry or cure the coating. The solvent evaporation may be acceleratedby vacuum removal coupled with fresh air or inert gas supply. Dependingupon the nature of the chosen coating, internal or external heat sourcesmay be used to accelerate drying. Further, for certain coatingchemistries, additional processing steps (imaging, hardening, fixing,etc.) may be necessary to make the coating fully resistant to thetargeted etching solution.

According to certain aspects of the presently disclosed invention, thehollow objects may be heated prior to application of the coating. Forexample, the hollow objects may be heated to a temperature of between140° C.-200° C., such as 150° C.-175° C., or even 160° C.-165° C. by anymeans known in the art (e.g., heating in oven, induction heating, etc.)prior to application of the coating. Application of the coating on thepre-heated hollow object may provide a faster cure of the coating, and amore uniform build of the coating.

For objects which are to be mechanically scribed and peeled, anadditional application of coating may be added after the correctthickness is achieved, or nearly achieved. This top application may beharder and of higher cohesive strength than the previous coatinglayer(s), and may improve mechanical peeling.

For objects which are to be patterned by laser ablation, wherein a laseris utilized to remove the coating, an appropriate colorant or dye may beadded to the coating formula to reduce the transparency of the coatingto the primary wavelength of the ablation laser, thereby maximizingenergy absorption and improving process efficiency. Further, thethickness of the coating may be matched to the characteristics of thelaser ablation equipment. In general, the thinnest application thatallows for full protection during the chemical or electrical millingstep is desired, as thinner coatings require less drying time, lesscoating material, lower laser intensities, and less time stripping thecoating after etching is complete.

For objects which are to be patterned using photoresist, the photoresistmay be applied to the inner surface of the object. Photoresist is aphotosensitive coating that changes properties when exposed to light,either gaining or losing resistance to attack by an etchant or solventin the areas exposed to electromagnetic radiation, most commonly in theUV light spectrum. The thickness and properties of the photoresist maybe matched to the equipment used for exposure of the pattern onto thephotoresist (e.g., photoresist may be chemically resistant and/orelectrically non-conductive).

For objects which are to be etched using a chemical etchant, the coatingmay be a coating resistant to the chemical etchant. Moreover, forobjects that are to be etched using EChE, the coating may be anelectrically non-conductive masking material or coating.

While several methods for coating the interior surface of the objecthave been described herein, other methods known in the art are withinthe scope of the present invention. Furthermore, more than one coatinglayer may be applied to the inner surface of the object, wherein eachcoating layer may vary in thickness and identity of the coatingmaterial. As previously indicated, selection of the specific coatingthickness and coating material may depend on at least the nature of theobject to be coated (i.e., material of the object), and/or on the methodof pattern generation to be used in future steps of the process.

According to certain aspects of the presently disclosed invention, thethickness of the coating may be substantially uniform on the interiorsurface of the object. For example, the coating used in a laser ablationprocess would be optimized to be as thin as possible to facilitatecomplete and uniform removal. Conversely, the coating used in amechanical scribe and peel process would be thicker because the cohesivestrength of the coating is relied upon to promote easy peeling of thecoating.

ii) Pattern Generation

The term “pattern generation” generally describes various methods andimplementations used to remove a portion of the coating from theinternal surface of the hollow object according to a specific pattern ordesign. The pattern may be preset or programmed into a computer (e.g.,translated from CAD drawings) which directs the movements of the variousdevices used to remove the portion of coating and movements of thehollow object, either together or individually.

A scribing device, be it a mechanical or laser device, may be includedas part of a larger system which includes a rotating apparatus 50, asillustrated in FIGS. 6A and 6B. Shown in FIG. 6A is a hollow cylindricalobject 20 which is supported on roller bar(s) 615 on one end of amounting stage 610. The object 20 may rest on and be rotated by theroller bar(s) 615. In certain instances, the object 20 may be secured,such as on a support or on the roller bar(s) 615 by a strap or belt (notshown). Rotation of the object 20 on the roller bar(s) 615 may be drivenby a motor 620. A scribing device, such as the mechanical scribingdevice 10 shown in FIGS. 1A-1D, or a laser machining device as shown inFIGS. 2A-2E, 8A-8C, and 9A-9C, may be included at an opposite end of themounting stage 610. Also shown in FIG. 6A is a rail 130 which mayprovide lateral movement of the scribing device (along longitudinal axisof the rail), and which may be rotated by a motor 625. Either, or both,motor 620 and 625 may be manually or automatically controlled, such asby speed controllers 630 and 635, respectively.

Show in FIG. 6B is the mechanical scribing device 10 positioned withinthe interior of the hollow object 20. Movement of the mechanicalscribing device 10 laterally to any position within the interior of theobject 20 may be motor controlled, either manually or automatically.While it is shown that mechanical scribing device 10 has longitudinalmovement on the mounting stage 610, it is also possible that the hollowobject 20 may be moved longitudinally on the mounting stage 610, or boththe device 10 and the object 20 may have longitudinal movement on themounting stage 610. Furthermore, either or both of the mechanicalscribing device 10 and the mounting stage 610 may provide movement inother directions, such as perpendicular to a longitudinal axis of therotating apparatus 50 and/or the rail 130 (“sideways” or “up-down”movements). Moreover, while a mechanical scribing device (10) is shownin FIGS. 6A and 6B, any of the laser machining devices detailed hereinmay be substituted to provide means for patterning the interior surfaceof the hollow object.

Alternatively, the system may include a mounting stage 205, as generallyshown in FIGS. 2A and 3A, which supports the hollow object vertically.As shown in FIG. 2D, the mounting stage may provide rotational movement(arrow 240) and/or longitudinal movement (i.e., vertically up or downalong the direction of arrow 250 b) of the hollow object. Opposite thismounting stage may be an additional stage or support for the scribingdevice (shown as a laser in FIGS. 2A and 2D), which may providerotational movement (arrow 240) and/or longitudinal movement (i.e.,vertically up or down along the direction of arrow 250 b) of thescribing device.

Described below are several exemplary devices and methods according tothe presently disclosed invention for pattern generation. Such devicesand methods include at least mechanical scribing and peeling, laserablation, and photoresist processes.

a. Mechanical Scribing and Peeling Process and Device

According to certain aspects of the presently disclosed invention, atleast a portion of the coating on the inner surface of the hollow objectmay be removed in a specific pattern using mechanical scribing. Suchmechanical scribing may be accomplished by use of a device according tothe present invention.

With specific reference to FIGS. 1A-1D, a scribing device according tothe present invention is shown, generally designated by reference number10. The device 10 includes at least one scribing blade, and preferablytwo independent scribing blades (110 a, 110 b) mounted in a blade holder106. The blade holder 106 may support as many blades, angled in as manydirections, as are necessary to achieve the desired pattern. When thecoating is to be scribed and peeled, it is typical for two scribingblades to be positioned adjacent one another to cut parallel linesoutlining the area to be peeled. As such, the distance between adjacentscribing blades may be varied so that different thicknesses of outlinedareas may be produced. Such variation may be manual, may be preset onthe blade holder 106, or may be automated and controlled by an automatedcontroller.

The blade holder 106 may be rotatably attached to a cutting head 100 ata distal end of the cutting head 100. Rotation of the blade holder 106may be about an axis which is perpendicular to a longitudinal axis 170of the cutting head 100. At least one tensioning spring (160 a, 160 b)may be used to tension the blade holder 106 to an engaged position onthe cutting head 100, as shown in FIGS. 1A-1C. The blade holder 106 maybe adjusted to a retracted position, as shown in FIG. 1D, using at leastone adjustment cord (150 a, 150 b) which counters the tensioning forceof the at least one tensioning spring (160 a, 160 b) and places theblade holder 106 in a position substantially parallel with thelongitudinal axis 170 of the cutting head 100. The engaged position ofthe blade holder 106 may be substantially perpendicular to thelongitudinal axis 170 of the cutting head 100. A stop or othermechanical block may be included on the cutting head 100 to limit theengaged position of the blade holder 106 to the substantiallyperpendicular position.

According to certain aspects of the presently disclosed invention, thescribing blade(s) (110 a, 110 b) may be standard or modified surgicalblades, which may be used to ensure minimal friction and standardizedscribing results.

One end of the tensioning spring(s) (160 a, 160 b) may be attached tothe blade holder 106 at a distal end of the blade holder 106, and/orproximal to the scribing blade(s) (110 a, 110 b). This attachment pointmay be along sides of the blade holder 106, as shown in FIGS. 1A-1D, ormay be on an inner surface 107 of the blade holder 106. The opposite endof the tensioning spring(s) (160 a, 160 b) may be attached to a proximalend (165 of FIG. 1D) of the cutting head 100. In this way, thetensioning spring(s) (160 a, 160 b) may provide tension that holds theblade(s) (110 a, 110 b) engaged with, i.e., in contact with, the innersurface of the object during mechanical scribing (i.e., biases the bladeholder 106 to the engaged position). The tension may be adjusted toaccount for varying coating thickness and/or hardness by replacing thetensioning springs (160 a, 160 b) with springs that have a differentspring rate.

The blade holder 106 may be “retracted” by countering the tension of thetensioning springs (160 a, 160 b) using one or more adjustment cord(s)(150 a, 150 b). That is, the adjustment cord(s) (150 a, 150 b) mayprovide a pulling force counter to the direction of tension provided bythe tensioning spring(s) (160 a, 160 b). One end of the adjustmentcord(s) (150 a, 150 b) may be attached to the blade holder 106, such ason an outer surface of the blade holder 106 opposite the inner surface107, and proximal to the scribing blade(s) (110 a, 110 b), such as alongposition 108. An opposite end of the adjustment cord(s) (150 a, 150 b)may be attached to a motor or other manual pulling device (not shown).As shown in FIG. 1B, the adjustment cord(s) (150 a, 150 b) may bedirected through a path that keeps the cord(s) in position during use.As such, the adjustment cord(s) (150 a, 150 b) may be used to adjust aposition of the blade holder 106 and scribing blade(s) (110 a, 110 b)through an arc that extends from the engaged position of the bladeholder 106 to the retracted position of the blade holder 106.

While springs and/or cables are shown to provide the tension and counterforce needed to position the scribing blades, other means to accomplishthis action are envisioned and within in the scope of the presentinvention. For example, a motor/gear driven apparatus may be used toposition the cutting blades between retracted and engaged positions.Furthermore, if space permits, pneumatic or hydraulic cylinders could beused to engage and disengage the blades with the object's interior tocontact the inner surface.

The cutting head 100 may be attached to a stage 120 that is operablyconnected to a rail 130 which allows lateral movement of the stage 120.As shown in FIGS. 1A-1D, the rail 130 may be a screw and the stage 120may be part of, or mounted on, a ball screw nut 125 which provideslateral movement of the stage 120 when the screw 130 is rotated by motor625. Further, the device may include a platform 140 which supports endsof the rail 130 and may further enable varying degrees of tension to beactuated between the scribing blades (110 a, 110 b) and the innersurface of the hollow object. The ball screw nut 125 may rotate withinthe stage 120, or the stage may be supported by the platform 140. Thatis, the stage 120 may ride on edges or sides of the platform 140 so thatthe stage 120 does not rotate with the rotation of the ball screw nut125 on the screw (rail 130). In this way, smooth lateral movement of theblade holder 106, cutting head 100, and stage 120 may be enabled anddriven manually or by a motor (e.g., the stepper motor 625 of FIGS.6A-6B; lateral movement is along a longitudinal axis 175 of the platform140). The motor may be speed controlled by an operator or by anautomated controller, such as speed controller 635 shown in FIGS. 6A-6B.

As discussed above, and shown in FIGS. 1A-1D, the rail 130 may be ascrew and the stage 120 may be attached to the screw via a ball screwnut 125 which provides lateral movement of the stage. Alternatively,lateral movement of the stage 120 may be actuated by a pulley system,belt drive, linear thruster, electric or pneumatic cylinder, or by anymeans known in the art. In the case of a pulley system, the rail 130 maybe used to hold the stage 120 in a specific position (e.g., by inclusionof guides), and the platform 140 may be optional. Alternatively, thestage 120 may ride on edges or sides of the platform 140, and the rail130 may be optional.

The cutting head 100 may be rotatably mounted on the stage 120 toprovide rotation of the cutting head 100, and thus the scribing blade(s)(110 a, 110 b), about an axis perpendicular to the longitudinal axis 175of the stage 120/platform 140. The position of the cutting head 100 withrespect to the stage 120 may be fixed, such as by a set screw 186, asshown in FIG. 1B, or by a pair of set screws (not shown). For example,an arm 180 may be used to support a set screw 186 which acts as amechanical stop, and a spring 182 may be used to limit rotation of thecutting head 100 away from the limiting position set by the set screw186. As indicated above, while a specific exemplary implementation isdescribed herein above, other means to accomplish rotation of thescribing blade(s) (110 a, 110 b) with respect to the stage 120 or rail130 are envisioned and within the scope of the present invention. Forexample, rotation of the blade holder 106 on the cutting head 100 ispossible, wherein a rotational position may be altered manually or maybe automatically controlled, such as through motors/gears, etc.Furthermore, rotation of the cutting head 100 on the stage 120 may usemotors and/or gears, and may be altered manually or may be automaticallycontrolled.

Prior to mechanical scribing and peeling, a scribing pattern may be setby an operator. The scribing pattern may include adjusting the linearspeed of the stage 120 with respect to the rail 130 and/or platform 140,and the rotational speed of the object to attain a desired pattern. Thescribing blade(s) (110 a, 110 b) may be retracted when the blade holder106 is placed in the retracted position using the adjustment cord(s)(150 a, 150 b), and the device 10 may be inserted into the hollow cavityof the object through an opening to a predetermined starting position.Mechanical scribing may then be achieved by movement of the device 10,and thus the scribing blade(s) (110 a, 110 b), along the inner surfaceof the hollowed portion of the object as the object is turned on arotating apparatus.

The rotating apparatus 50 may be a separate portion of the device10(such as the mounting stage 610, roller bars 615, motor 620, andsupport rail 610 shown in FIGS. 6A and 6B) or may be integral with thedevice 10, such as a support stage (not shown) at a distal end of theplatform 140 configured to support the object on a bottom surfacethereof, and/or an attachment end (not shown) at a distal end of therail which provides rotation of the object when in contact with a bottominner surface of the object.

According to certain aspects of the presently disclosed invention, thecutting speed may be determined based on the underlying object materialand coating(s) characteristics. With regard to a cylindrical object, astraight line running parallel to the center line of the object may bescribed by the straight movement of the cutting head and stage (100 &120) from the starting point within the object, without any rotation ofthe underlying apparatus or object. As the cutting head and stage (100 &120) moves along the ball screw 130, the blade(s) 110 a, 110 b makecontact with the coated interior surface and will scribe a straight lineas far as the cutting head and stage (100 & 120) is moved within theobject. Alternatively, rotating the object 20 without moving the cuttinghead 100 will result in a circumferential line. Combining the twomovements will allow a helical design to be achieved by the straightmovement of the cutting head and stage (100 & 120) within the object 20as it turns on the rotating apparatus 50. The blades 110 a, 110 b areeasily retracted using the adjustment cord(s) (150 a, 150 b) asnecessary to create breaks in the scribed lines.

After scribing, the cut pieces of coating may detach from the underlyingmaterial of the object (e.g., metal), and may be removed by any meansknown in the art. For example, high pressure air or solvent (e.g.,water) may be used to blow the cut pieces out of the interior of thehollow object. This process, termed peeling, may also be accomplishedwith a scraping piece which may be affixed to the device 10 in place of,or mounted between, the scribing blades. Manual peeling may also beaccomplished by hand using a small pick.

b. Laser Ablation

According to certain aspects of the presently disclosed invention, atleast a portion of the coating on the interior surface of the hollowobject may be removed in a specific pattern using a laser ablationprocess. This process utilizes a laser to vaporize the coating to exposethe desired pattern(s). Vaporized coating gas may be exhausted away fromthe laser to prevent re-depositing of particles.

With reference to FIGS. 2A-2E and 3A-3B, the laser ablation systembroadly consists of three parts: i) a laser body and cooling system 40;ii) an access arm 334 with reflector 365, final focusing lens 360,optional proximity sensor 368, supply gas 330 and an evacuation system332 (collectively 30); and iii) a multi axis moveable stage 205 uponwhich the hollow object 20 rests. The laser body and cooling system 40(i.e., laser source 40) generally comprises a laser generating systemincluding any one or more of a laser diode, laser oscillator, fiberoptic cable, laser resonator, laser collimator lens, etc. For example,according to certain aspects of the present invention, the laser sourcemay general a beam that is passed via a fiber optic cable to acollimator lens housed in the region labelled with reference number 40.The reflector 365, and in some cases the focusing lens 360, may bereferred to as the laser head 30.

While shown as a stage 205 that supports a base of the hollow objectlongitudinally (e.g., hollow object is supported in an upright verticalposition), other support structures and orientations are within thescope of the presently disclosed invention. For example, the multi axismoveable stage 205 could support the hollow object 20 in a horizontalposition with the laser head 30 entering through the opening 220 on ahorizontal plane.

The object 20 may be placed against a reference point on the moveablestage 205 which may hold the object stationary, or may provide rotationof the object, such as shown by arrow 240, and/or may provide lateral(arrow 250 a) and/or longitudinal (arrow 250 b) movement of the object.In various implementations, the laser may be stationary while the objectrotates/moves around it, the object may be stationary while the laserrotates/moves within it, or the laser may move in one or more dimensionswhile the object moves in one or more dimensions, the two sets ofmovements coordinated by manual manipulation or through automatedcontrols.

The laser head 30 may be passed through an opening 220 in the object 20(see FIG. 2A), to a specified position (FIG. 2B). A sensor 368 mountedadjacent to the reflector 365 may continuously read a distance between acoating layer 210 on an inner surface of a wall 200 of the object 20 andthe reflector 365, and the moveable stage 205 may adjust the positionaccordingly to maintain a constant distance (i.e., the focal length) ofthe laser from the coating surface to be patterned (FIG. 2C). Thisconstant focal length may provide full ablation of the coating down tothe interior surface of the hollow object 20 while minimizingdistortions of the ablated coating edges. The stage 205 may be rotated,and moved either laterally and/or longitudinally, to provide etching ofthe pattern on the interior coated surface 210 of the object (FIGS. 2Dand 2E). Alternatively, or additionally, the laser head 30 may also berotated, and moved either laterally and/or longitudinally, to provideetching of the pattern on the interior coated surface 210 of the hollowobject 20.

The supply gas 330 and evacuation system 332 may be designed to pump athigh volumes to effectively remove all of the vaporized coatingcomponents in real time to prevent deposition of contaminants onto thelenses. Argon gas (or other suitable gas) may be used as the supply gasto further inhibit contaminant compound formation on the lenses and toprevent the formation of compounds at the object surface that may alterthe etch rate.

The dwell time of the laser beam on the coating may be dependent on boththe coating characteristics and the laser characteristics (mostsignificantly, laser intensity), and can range from several inches perminute up to three or more feet per second. Further, the desiredablation width may be driven by the laser beam width, or by additionalmanual or programmed patterns. For example, a narrow beam can create awider ablation width through a program that moves the beam rapidly backand forth laterally as it progresses. This method requires a lowerintensity laser than a beam already of the required final ablationwidth, but is limited to lower ablation speeds as a result of thenecessary continual lateral movements.

To optimize a laser process for ablating (or welding, cutting, etc.),the collimated beam from the laser source may be focused by a focusinglens (converging lens). This will result in an optimal spot, a specificdistance away from the lens. The distance between the lens and thatoptimal spot is referred to as the focal length (f) of the lens. Formaximum ablation efficiency and to keep the spot size consistent, thefocal length should be kept constant. This means the focus lens must bekept a fixed distance away from the surface to optimize the ablationprocess.

With specific reference to FIG. 7, a laser beam 705 may be focused to aspecific focal length 715, beam diameter 725, and depth of focus 720 bya focusing lens 710, so that a focal point 750 of the beam is positionedon a surface to be patterned. As indicated above, as the distancebetween the focused laser beam (i.e., focusing lens 710) and thesubstrate to be patterned changes, the position of the laser beamrelative to the substrate must also change so that the focal point 750remains positioned, i.e., focused, on the substrate at least within thedepth of focus 720. If the substrate is moved such that the beam is nolonger focused on the substrate, the laser may not function efficientlyor properly to ablate or add material in the defined pattern. Thisbecomes an issue when ablating the inside of a container with a radiusless than the focal length of the lens. To resolve this issue, areflector may be inserted between the focus lens and the surface to beablated. The sum of the distance between the focus lens and reflectorand the distance between the reflector and the surface to be ablatedmust be equal to the focal length.

With reference to FIGS. 8A-8C, the hollow object 20 may have an internalprofile defining one or more internal diameters. For example, the hollowobject 20 may have an opening 220 having an internal diameter 220A thatdiffers from a diameter of a lower or main body portion 220C of thehollow object 20. Moreover, other internal profiles of the hollow objectmay be non-uniform (e.g., sloped, ridges, etc.), such as region 220B. Assuch, a distance from the focused laser beam, such as beam 360 shown inFIG. 3B, to the interior surface of the hollow object (210A, 210B, 210C)may change as the beam is moved laterally or rotationally within thehollow object.

This change in distance, such as to distances that are greater than orsmaller than the focal length 715 of the laser beam 705, may beaccommodated by changing the focusing lens 710 to one having a differentfocal length 715 (i.e. focal length matched to the distance between thefocusing lens 710 and the substrate). Such a solution would not befeasible, however, for patterning inclined or non-uniform surfaces, suchas the sloped surface 210B shown in FIGS. 8A-8C.

Alternatively, as shown in FIG. 2D, a stage on which the hollow objectrests (e.g., the moveable stage 205 of FIG. 2A) may provide lateral(arrow 250 a) movement of the object, or the laser head 30 may be movedlaterally to be closer to or farther away from the surface to bepatterned. If, however, the opening 220 is small, such movement may notbe possible as the amount of lateral movement 250 a required may exceedthe diameter of the opening 220. The presently disclosed inventionsolves this problem by providing a system that changes the lateralposition of the focal point 750 without changing the lateral position ofthe laser head 30 or the focal length 715 of the focused laser beam.

With reference to FIG. 9A, the laser beam may be focused by a lens(focusing lens 815) and deflected toward the substrate surface 210A by areflector 835. To deflect the focused laser beam by 90 degrees, areflector 835 positioned at an angle of 45 degrees to the laser beam(705 of FIG. 7) may be used, as shown in FIG. 9A (i.e., angled 45degrees to the longitudinal axis of the laser system). The focal lengthf of the focused laser beam is therefore the distance A from thefocusing lens 815 to the reflector 835 plus the distance B from thereflector 835 to the focal point of the lens (i.e., see 750 in FIG. 7).Optimally, the second distance B will equal the distance between thereflector 835 and the inner wall of the hollow object 210A so that thefocal point 750 is focused on the inner wall of the hollow object 210A.Thus, as shown in FIG. 9A, the focal length f may equal A₁+B₁.

While a specific angle for positioning of the reflector 835 isindicated, i.e., 45 degrees, other angles are possible and within thescope of the presently disclosed invention. For example, the reflector835 may be positioned at different angles to change the distance B fromthe reflector 835 to the focal point of the lens, or to position thefocal point of the lens around or past an internal feature in the way ofthe straight path of the lens (i.e., overhanging feature).

As indicated in FIG. 9A-9C, the inner wall of the hollow object 20 mayhave a non-uniform shape, and thus the distance between laser head 30and the reflector 835 may not remain constant. For an exemplary hollowobject 20, the inner wall may slope outward, such as shown for region220B in FIG. 9B, so that the reflector 835 is now further from the innerwall 210B. In FIG. 9C, the diameter 220C of a lower region of theexemplary hollow object 20 may be greater than the diameter 220A of anopening 220 of the hollow object 20 such that lateral movement of thelaser head (including the laser arm 805 and laser source 40) may notcompensate for the increased distance B3. In this case, in order tomaintain the relationship f=A+B, when the distance B becomes larger, thedistance A must be made inversely smaller. Thus, as shown in FIGS. 9Band 9C, as the laser head 30 moves longitudinally into the interior ofthe hollow object, and the distance between the reflector 835 and theinner wall of the hollow object A changes, the distance B between thefocusing lens 815 and the reflector 835 will also be changed:

f=A ₁ +B ₁ =A ₂ +B ₂ =A ₃ +B ₃

As indicated, the distances A and B are inversely proportional so thatthe focal length f remains constant.

According to certain aspects of the presently disclosed invention, thedistances A and B may be varied by changing a distance between thefocusing lens 815 and the reflector 835. The presently disclosed lasersystem may include an inner tube 810 comprising the laser source 40 orat least a collimating lens at a distal end, and a focusing lens 815 ata proximal end (e.g., laser generator connected to collimator lens via afiber optic cable). This inner tube 810 may be moveably nested within anouter tube 812 comprising the reflector 835 at a distal end, wherein thefocusing lens 815 is positioned closest to the reflector 835. In thismanner, longitudinal movement (i.e., arrow 800) of the inner tube 810within the outer tube 812 will change the distance A between thefocusing lens 815 and the reflector 835. As the distance A changes, forexample to become shorter, the distance B between the reflector 835 andthe focal point of the laser beam may also change (i.e., become longer).As such, the laser beam may remained focused on the inner surface of thehollow object without lateral movement of the laser system (arrow 801).

As shown in more detail in FIGS. 9A and 9B, the outer tube 812 mayinclude one or more stops or surfaces (816, 840) which limit thelongitudinal motion of the inner tube 810 therein. For example, aprotruding surface 814 of the inner tube 810 may contact an innersurface 816 of the outer tube 812. This stop acts to provide a lowerlimit to the distance A, and as such defines the maximal length of thedistance B (B3 in FIG. 9C). Similar physical stops (not shown) orelectronic stops may be provided which place an upper limit on thedistance A, and thus provide a minimal length for the distance B.Accordingly, the range of distance B is only limited by the positioningof the stops which limit movement of the focusing lens 815 relative tothe reflector 835, and/or the maximal focal length of the focusing lens815. As such, methods for patterning an interior surface of a hollowobject may be accomplished using the presently disclosed laser systemand a single focusing lens.

In certain circumstances, objects having very large changes in theinternal diameter may need to be patterned, wherein the differences indiameter may exceed the maximal/minimal length of the distance Bprovided by a single focusing lens. Thus, additional focusing lenses maybe used, wherein a motion control system may assist in patterning thoseregions accessible by the system having a first focusing lens during afirst patterning cycle, and those regions accessible by the systemhaving a second focusing lens in a second patterning cycle, etc.

The linear motion between the inner tube 810 and the outer tube 812 maybe actuated by a ball screw controlled by a servo motor, which may be inelectronic communication with a server (controller 900 in FIG. 10). Theserver may be configured to store or receive dimensional data of aninternal shape of the hollow object, and control the servo motor basedon the dimensional data. While a specific means for providing linearmotion of the inner tube relative to the outer tube, e.g. a ball screwactuated by a servo motor, is disclosed herein, additional means forproviding this movement are known in the art and within the scope of thepresently disclosed invention.

The laser system shown in FIGS. 9A-9C may be adjusted using a motioncontrol system which may be a separate part of the overall system, ormay be part of the system that controls rotational and translationalmotions about the longitudinal axis of the hollow object and/or thelaser system. That is, the motion control system may provide rotationabout a longitudinal axis and translation along the longitudinal axis(i.e., depth of entry of the laser head into the interior of the hollowobject) for one or both of the hollow object and the laser system basedon the complex pattern. The motion control system may also change apositional relationship between the reflector 835 and the focusing lens815 to accommodate a change in a distance between the reflector 835 andthe interior surface of the hollow object so that the focal point of thelaser system remains focused on the interior surface.

The change in the positional relationship may be based on real-timedimensional data of the distance between the reflector and the interiorsurface of the hollow object collected by a position sensing deviceattached to the laser system. An exemplary position sensing device isshown in FIG. 3A (368), and measures a real-time distance to asubstrate. The term real-time may be understood as a time scaleconsistent with the time scale of the laser machining methods disclosedherein, so that the focal point of the laser may remain focused on thesubstrate as the laser head is moved to different positions on thesubstrate.

As shown in FIG. 10, an exemplary system for laser machining accordingto the present invention may include a laser system 912 (laser source,collimator, focusing lens, reflector, etc.), a motion control system902, a controller 900, and a user interface 914. A memory 906 of thecontroller 900 may store computer-executable instructions executable bythe processor 904, and configured to direct motor(s) 908 of the motioncontrol system 902 to adjust the positional relationship between thereflector 835 and the focusing lens 815 based on the real-timedimensional data acquired by the sensor(s) 918 of the laser system 912(motor 908 may include the servo motor that actuations the screw ballconnecting the inner 810 and outer 812 tubes of the laser system).Additional sensors 910 may be included as part of the motional controlsystem for verification of object placement and/or movement, and/orlaser system position and/or movement.

Alternatively, the change in the positional relationship may be based ondimensional data of an interior shape of the hollow object stored on aserver. The controller 900 may store the dimensional data on a memory906, along with computer-executable instructions configured to directmotor(s) 908 of the motion control system 902 to adjust the positionalrelationship between the reflector 835 and the focusing lens 815 basedon the stored dimensional data. A user interface 914 may be includedthat may provide direct user communication with the controller 900, andmay provide a means to input dimensional data related to a specifichollow object.

According to certain aspects of the presently disclosed invention, thestored dimensional data may be data acquired and stored from previous“scans” of a hollow object, such as from the sensor 910 during a priorablation process, and may include a map of an internal shape of thehollow object, or a map of the internal shape of the hollow object inonly those regions relevant for machining the complex pattern.

The adjustment mechanism disclosed herein may provide a system capableof changing the lateral position of the focal point of a laser withoutchanging the lateral position of the laser head or the focal length ofthe focused laser beam. By making the distance between the focusing lensand reflector adjustable, the system can accommodate containers ofassorted sizes subject to the focal length of the specified lens. Thisadjustability also allows for laser patterning or ablation inside oftapered containers (or containers with changing radius) by moving thefocusing lens away from the reflector as the surface gets closer to thereflector or by moving the focusing lens towards the reflector as thesurface gets further away from the reflector. The adjustability of thefocus lens can be motorized and programmable based upon a container'sdesign.

As such, the presently disclosed systems may be able to pattern theinterior surfaces for objects that were previously not possible usingthe methods and system so the prior art. For example, for a hollowobject having a small opening having a diameter less than an interiordiameter of a main body portion of the hollow object, it would not havebeen possible to move the entire laser head 30 to a position within thesmall opening that would maintain the laser focused on the interiorsurface of the lower interior regions of the hollow object.

Accordingly, the present invention relates to methods for forming acomplex pattern on an interior surface of a hollow object having a smallopening, wherein a diameter of the small opening of the hollow objectmay be 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10% or less than aninterior diameter of the hollow object. The method comprises passing alaser system through the small opening of the hollow object so that afocal point of the laser system is focused on the interior surface ofthe hollow object, wherein the laser system comprises a reflector toangle the focal point ninety degrees with respect to a longitudinal axisof the laser system onto the interior surface of the hollow object. Bothrotational and/or translational movement are provided along alongitudinal axis for one or both of the hollow object and the lasersystem based on the complex pattern. The laser system is then operatedto form the complex pattern on the interior surface of the hollowobject. A longitudinal distance between the reflector of the lasersystem and a focusing lens of the laser system may be changed toaccommodate a change in a lateral distance between the reflector and theinterior surface of the hollow object so that the focal point remainsfocused on the interior surface.

The adjustment of the longitudinal distance between the reflector andthe focusing lens may be provided by a motion control system based onreal-time dimensional data of the distance between the reflector and theinterior surface of the hollow object collected by a position sensingdevice attached to the laser system, or based on dimensional data of aninterior shape of the hollow object stored on a server.

An exemplary laser incorporates a 250-500 mm effective focal length,0.040″ focused point diameter, 1 kW fiber pulsed laser, with flattopbeam shaping for uniform ablation across the removal width. This methodpermits the same flexibility in interior pattern design as mechanicalscribing and peeling, but may provide greater accuracy and efficiency asthe laser process may be more highly automated and computer driven,permitting tighter tolerances and significantly shorter processingtimes.

While the pattern generation detailed hereinabove has been discussed interms of systems and methods for patterning interior surfaces of hollowobjects, the systems and methods are equally applicable to patterningexterior surfaces. For example, rather than supporting the object to bepatterned on a rotating apparatus 50 such as shown in FIG. 6A, whereinthe patterning device is supported on a rail 130 that enters the hollowcavity, the object may be support in a manner wherein the patterningdevice maintains access to an exterior of the object (e.g., displacesupport 50 and rail 130 laterally).

c. Photoresist Process

According to certain aspects of the presently disclosed invention, atleast a portion of the coating on the interior surface of the hollowobject may be removed in a specific pattern using a photoresist process.This process utilizes a laser, much as described above, though possiblyat lower intensity and at differing wavelength, to expose the desiredpatterns onto a photoresist coating that is compatible (resistant to)the chosen etchant.

Photoresists can be broadly divided into two types; positive acting andnegative acting. With a negative acting photoresist, the coating may beapplied and dried at specific conditions, but is not yet cross-linked or“cured.” Exposure to a specific wavelength of electromagnetic radiation(EMR) energy, typically in the UV range of the spectrum, causes theresist to cross-link where exposed, becoming insoluble to the specificdeveloping solution. The areas not exposed to the specific EMR energywill freely wash away when exposed to a developing solution, exposingthe substrate material (surface of the object) to allow for etching.

With a positive acting photoresist, the dried coating exhibits theopposite behavior as described above. The positive acting photoresistwill become soluble where exposed to the EMR energy, and remaininsoluble where not exposed. According to certain aspects of the presentinvention, a device similar to the laser ablation device describedherein, though at differing energy wavelength and intensity, may be usedwith a positive photoresist process for internal etching. As described,the device may be automated to provide highly efficient and accuratepattern formation on the interior surface of a hollow object. That is,the patterns may be preset or programmed into a computer (e.g.,translated from CAD drawings) which directs movement of the laser head30 and movement of the object 20 on the moveable stage 205 (see FIGS. 3Aand 3B), either individually (the laser within the stationary object, orthe object around a stationary laser), or together.

After exposure to the laser, the pattern may be developed using theappropriate chemistry. For the positive photoresist process, thisdevelopment step removes the photoresist in the areas required to beetched to reveal the underlying object surface. After the pattern hasbeen developed, the photoresist may be hardened using the appropriatemethod (chemical, light exposure, temperature, etc.) to keep it fromwashing away during etching.

The equipment for exposing the pattern into the photoresist is similarto the laser ablation system, but produces a beam of the correctwavelength to expose the photoresist, typically runs at significantlylower intensities (as it only needs to crosslink chemistry and notvaporize the coating), may not require a gas supply and exhausting (asno vaporized particles are created), and may not need edge sensingfeedback and continuous positioning correction to preserve the laserfocal length, as more latitude in exposure is typically expected forthis type of processing. The laser system would still consist of, at aminimum: i) a laser body and potentially a cooling system; ii) an accessarm with reflectors and final focusing lenses; and iii) a multi axismoveable stage upon which the object rests. The object may be placedagainst a reference point on the moveable stage.

In addition to the laser exposure steps outlined above, this method mayalso require two additional steps: i) Developing and ii) Hardening (eachdefined below). In some instances, the addition of these two steps maycause this alternative to be both costlier and more time consuming thanlaser ablation.

The developing process generally consists of dipping the object in achemical, and/or spraying the chemical into the hollow interior of theobject, to dissolve the uncured or non-cross-linked photoresist andreveal the underlying surface in the selected pattern (“developing”).Parameters and developing chemistry generally vary with photoresistcharacteristics and thickness.

After developing, the remaining resist may be fixed in place(“hardening”) to prevent it from being washed away during the upcomingetching process. Depending upon the resist selected, this may beaccomplished chemically, thermally, or with a combination of the two.The chemical hardening process generally consists of spraying or fillingthe hollow interior of the object with a chemical which reacts with theresist to cause it to become insoluble to the selected etchant. Sprayingapparatus such as detailed below, and shown in FIGS. 4A-4B and 5A-5E maybe used. The thermal hardening process is generally accomplished bybaking the object with the resist coating at an elevated temperature fora prescribed length of time. Parameters and hardening chemistry willvary with photoresist characteristics and thickness. Care must also betaken when using thermal hardening to ensure that the process iscompatible with the substrate as to not affect its physical properties.

iii) Etching

The patterned object, whether produced through laser ablation,mechanical scribing and peeling, or by a photo resist process may beplaced on a motor driven, speed controlled, rotary stage with sprayheaders which may be matched to an interior cavity geometry of thehollow object. With specific reference to FIGS. 4A-4B, the object 20 maybe supported by a strap or belt 415 having a gear that may interact witha secondary gear 410. As such, rotation of the object, shown as arrow440, may be driven by an axle 408 and motor (not shown). Alternatively,the object 20 could be supported on a stage, such as stage 205 shown inFIGS. 2A-2E.

A spray header 400 having various nozzles 420 may be placed within theinterior cavity of the object 20 to provide an etchant solution to theinner surface of the object. The design of the spray header 400 (andnozzles 420) must be carefully evaluated for specific object geometriesand etchants.

In designing the spray header 400 to deliver the etching solution to theinner surface of the object 20, several design considerations werestudied:

The etch rate, which may depend, in part, on the spray pressure of thenozzles 420 in the header 400, the spray volume of those nozzles 420, orboth. Further, the spray volume (flow rate) of the nozzles 420, which isa function of spray pressure. Moreover, if internal pressure is appliedto assist in evacuation of the spent etchant from the interior of theobject, the spray pressure in the nozzles 420 and/or the spray volume ofthose nozzles 420 may need to be adjusted to counter the internalpressure.

The type of nozzle 420, which may affect the etch rate and etch pattern.Full cone nozzles, in either round or square configuration, aregenerally considered the optimal pattern, as they result in the highestcontinuous coverage of etch solution at the inner surface.

The placement of the nozzles 420 on the spray header 400, which may beconfigured to maximize coverage while minimizing destructiveinterference between individual nozzle cones. For ferric chlorideetching of the internal surface of cylindrical objects, for example, ahelical arrangement of nozzles was found to be optimal.

Movement of the object 20, which may be configured to occur with respectto the nozzles 420 to minimize the effect of the pressure (and flow)differential that occurs from the direct cone center, where pressure ishighest, to points further out the radius of the cone, where pressuredecreases further out toward the edges. For a cylindrical object with ahelical nozzle arrangement, the movement may incorporate rotating theobject around the spray header, while simultaneously oscillating thespray header vertically the same distance as the vertical distancebetween nozzles on the spray header.

While designing the spray header for etch rate and uniformity, severalconstraints were also considered:

While maximizing flow rate and pressure may improve etch rates, doing somay come at the expense of larger spray nozzles. For a cylindrical sprayheader etching a cylindrical object, the maximum diameter of the nozzlesmounted on the header must be smaller than the opening through which thespray header must travel. This may require specialized nozzles, designedand fabricated or modified for the particular application.

The spray header itself must be of a small enough diameter to allow forinsertion into the object with nozzles inserted (as above), but theinside diameter must be large enough to accommodate the flow rate ofetch solution necessary to minimize pressure differential between thenozzles on the header. That is, the inside diameter should besufficiently large to allow fluid velocity to be maintained atrelatively low levels (<20 ft/sec).

The outside diameter of the header should be small enough to allowsufficient open area between the outer diameter (OD) of the header andthe inner diameter (ID) of the object opening, to allow spent or reactedetch solution to flow back out of the object. If the open area is toosmall to allow the spent etchant to escape under gravity alone, then asmall diameter pressure tube may be fixed to the spray header and extendbeyond the end of the spray header into the object. This pressure tubemay then be pressurized with a suitable gas to pressurize the insidecavity, forcing the spent etchant out at an accelerated rate versusgravity alone.

Many of the design factors and constraints are in direct opposition toeach other, and so the design of a specific spray header system will bematched to the individual application, and the factors optimallybalanced against each other for the exact conditions of thatapplication.

Some combinations of etchants, substrates, and process variables maycreate patterns in the depth of substrate removed. This is referred toas “banding” due to its visual appearance. Banding can be minimized byeither moving the spray header or object on the longitudinal axis. Theamount of movement will depend on the distance between the nozzles, andthe frequency of movement should be out of sync with the rotationalspeed of the object.

The etch chemistry may be matched to the particular material of theobject and coating, and may be designed to optimize for the desiredfinal pattern attributes (depth, final width, surface roughness, etc.).The etchant may be sprayed through the nozzles 420 against the interiorsurface of the object. The parameters at which the etch solution itselfis provided (e.g., temperature, density, spray pressure, etc.) may becustomized to achieve the final pattern attributes. The etching solutiondissolves the material exposed through the preceding processes, as theetching process mills into the internal surface of the object along thepattern scribed.

In the case of a cylindrical object, the object may be placed on arotating stage with an adjustable rotation rate, such as 6 rpm. Thisrotation rate may be adjusted upward depending on the object diameter.Larger diameter objects may have larger internal circumferencesrequiring faster rotational speeds to maintain the same etch rate assmaller diameter objects.

For example, ferric chloride may be used as an etchant for ferrousalloys, sprayed at 5-300 pounds per square inch (psi) at a temperatureof 70-200° F. and specific gravity of 1.10-1.50. For example, ferricchloride may be sprayed at a pressure of 80 psi, a temperature of 140°F., and a specific gravity of 1.30. However, any etchant appropriate tothe underlying object surface and selected coating may be used tofacilitate this step of the method.

Etching parameters may change depending on the etchant chemistry andmaterial of the object being etched. Higher spray pressures may berequired for materials that contain components, or produce etchingbyproducts, that are insoluble to the selected etchant. For example,some steels contain higher concentrations of silicon, which is insolublein ferric chloride, and will require higher pressures to mechanicallyremove the silicon to keep it from decreasing or completely blocking theetching reaction. Depending on the material composition and the finalpattern geometry, this process can take anywhere from 10 minutes to over8 hours.

According to certain aspects of the present invention, the object may besubmerged in the etch solution for a prescribed time period to achievethe desired material removal. Submersion allows uniform removal of themetal to a desired depth where the coating was removed without the needfor a specialized spray header.

According to certain aspects of the present invention, if the objectmaterial is electrically conductive or can be made to be electricallyconductive, an electrochemical etching (EChE) process may be used. Insuch an instance, the coating may be an electrical insulator, and thepatterned object may be flooded with an electrolytic solution and mayhave a cathode inserted in the opening such that the cathode does notmake contact with the object. The hollow object may thus act as theanode, such that when an electric current passes through the electrolyte(between the anode and cathode), the surface of the hollow object in theexposed pattern is etched, i.e., the current will etch the exposedpattern by “plating” the object material, acting as the anode in thiscase, toward the inserted cathode in an electrochemical etching process.

The cathode may be shaped to match the general contour of the internalsurface to maintain constant distance and therefore constant resistancebetween the cathode and anode, or a simple geometric shaped cathode suchas a cylinder may be used and compensated with an insulating coating orcover applied selectively to achieve constant resistance across thecathode-anode gap. In such a process, newly introduced electrolyte maybe moved rapidly through the anode-cathode gap and out into an externaltank so that the removed material flows out into a settling tank insteadof plating to the inserted cathode. Alternatively, the removed materialmay simply be plated onto the cathode.

According to certain aspects of the present invention, the interiorsurface of the object can be electrochemically plated in a similar butopposite fashion as described above, wherein the object is the cathodeand the anode is made of the desired plating material. Current passesthrough the object to the anode resulting in the exposed interiorsurface of the object being plated with the desired material. Theprocess and equipment for electrochemical plating is well-known in theart but has been limited to flat plates, such as circuit boards andglass, entire surfaces of objects, or easily accessible surfaces. Theaforementioned process would allow detailed designs to be plated on theinterior of objects with restricted access such as pipes, tubes andconduits. Plating patterns on the internal surfaces of a pipe couldresult in increased flow turbulence, effectively an integrated staticmixer, or if desired improving laminar flow around high precisionin-line instrumentation, reducing the need for long straight runs ofpiping before the sensor element.

The EChE process detailed herein differs from electrochemical machining(ECM) where the desired pattern are formed primarily by the shape of thecathode in close proximity to the work-piece surface.

iv) Finishing

The inventive processes described above may further include a multi-stepfinishing procedure. Once etching is complete, the object may be rinsedclean of all residual etchant or electrolyte and placed in a bath ofstripping solution (a solvent matched to the coatings) to remove allremaining coating material. Alternatively, a wet blast processconsisting of high pressure sprays of a solution containing a suitableaggregate component could be used in place of the stripping solution tomechanically remove the coating from the object. After the remainingcoating is removed (“stripping”), the object may be thoroughlypressure-washed and dried in preparation for any required final surfacetreatments. Such treatment typically consists of passivation and/or oilcoating for ferrous alloy metal parts. Other materials may require othertreatments.

With reference to FIG. 5A-5E, such a process may include passing a highpressure spray head 510 through an opening 220 in the object 20 (seeFIG. 5A) to a defined position (see FIG. 5B). As shown in the figures,the object 20 may be supported on a stage that provides rotation, suchas shown by arrow 540, and longitudinal movement, such as shown by arrow550 (see FIG. 5C-5E). Alternatively, the spray head 510 may be moveablein a longitudinal and rotational manner to enable positioning of thespray head 510 within the interior of the object.

The spray head 510 may be activated to provide a solution (e.g., waterstripping solution) or solid material (e.g., sand, aluminum oxide, etc.)at a high pressure to an inner surface 210 of the object 20.

While the presently disclosed invention has been described in detail, itshould be appreciated by those skilled in the art that variousmodifications and alternations and applications could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular systems and methods disclosed are meant to be illustrativeonly and not limiting as to the scope of the invention.

For example, the presently disclosed methods and devices may be usefulfor etching patterns on the interior walls of specialized piping. Pipingflow could be manipulated by applying etch patterns, either to decreaseturbulence thereby increasing fluid flow efficiency, or conversely toincrease turbulence for mixing purposes by effecting a disruption in thepipe wall.

Moreover, both additive and removal processes, using any of laserablation, mechanical scribing and peeling, and photo resist methods, arehighly customizable for the purpose of accommodating novel shapes andspace restrictions and such customizations based on shape and space arecontemplated in these descriptions. Furthermore, laser ablation can bemated with computer automated systems and software to enable fullautomation of cutting with a controls platform that allows for easymodification of the ablation path and such mating is likewisecontemplated herein. Finally, though developed in the context of ferrousalloy metal objects, the processes herein described are for broadapplication for use in objects comprised of any material whatsoever.

What is claimed is:
 1. A method for forming an etched pattern on aninterior surface of a hollow object, the method comprising: positioninga laser system within the hollow object so that a focal point of thelaser system is focused on the interior surface of the hollow object;and operating the laser system to form a complex pattern on the interiorsurface of the hollow object, wherein motion of one or both of the lasersystem and the hollow object is controlled by a motion control systemconfigured to provide: (a) rotation about a longitudinal axis,translation along the longitudinal axis, or both for either or both ofthe hollow object and the laser system based on the complex pattern, and(b) adjustment of a positional relationship between a reflector of thelaser system and a focusing lens of the laser system to accommodate achange in a distance between the reflector and the interior surface ofthe hollow object so that the focal point remains focused on theinterior surface, wherein the change in the distance between thereflector and the interior surface is caused by a non-uniform shape ofthe interior surface of the hollow object.
 2. The method of claim 1,wherein an amount of adjustment of the positional relationship isinversely proportional to the distance between the reflector of thelaser system and the interior surface of the hollow object.
 3. Themethod of claim 1, wherein the motion control system provides adjustmentof the positional relationship based on real-time dimensional data ofthe distance between the reflector of the laser system and the interiorsurface of the hollow object collected by a position sensing device. 4.The method of claim 1, wherein the motion control system providesadjustment of the positional relationship based on dimensional data ofan interior shape of the hollow object stored on a server.
 5. The methodof claim 1, further comprising, before positioning the laser systemwithin the hollow object: applying a coating which resists etchants oracts as an electrical insulator to the interior surface of the hollowobject.
 6. The method of claim 5, wherein operating the laser system toform the complex pattern on the interior surface of the hollow objectcomprises ablating the coating in the complex pattern
 7. The method ofclaim 5, wherein the coating is a photoresist, and the method furthercomprises, after operating the laser system to form the complex patternon the interior surface of the hollow object: treating the photoresistwith a developing chemical to remove the photoresist in the complexpattern.
 8. The method of claim 5, further comprising, after operatingthe laser system to form the complex pattern on the interior surface ofthe hollow object: etching the interior surface of the hollow object inthe complex pattern by an electrochemical etching (EChE) process,wherein the EChE process comprises exposing the interior surface of thehollow object to an electric current in the presence of an electrolytesolution.
 9. The method of claim 5, further comprising, after operatingthe laser system to form the complex pattern on the interior surface ofthe hollow object: etching the interior surface of the hollow object inthe complex pattern by a chemical etching process, wherein the chemicaletching process comprises applying an etching agent that chemicallymills the interior surface of the hollow object in the complex pattern.10. The method of claim 5, wherein applying the coating to the interiorsurface of the hollow object comprises: applying the coating through aspray gun to the interior surface of the hollow object until a desiredcoating thickness is achieved, wherein the spray gun, the hollow object,or both rotate; pouring the coating into an interior of the hollowobject and rotating the hollow object at a speed sufficient to provide auniform coating distribution in the interior surface thereof pouring thecoating into the interior of the hollow object in an amount sufficientto fill the interior of the hollow object, and inverting the hollowobject to allow the coating to drain; or a combination thereof
 11. Themethod of claim 5, further comprising: applying the coating to anexterior surface of the hollow object.
 12. The method of claim 9,wherein applying the etching agent comprises: submerging the hollowobject in the etching agent for a period of time sufficient to mill theinterior surface in the complex pattern to a desired depth; or sprayingthe etching agent from a spray header, wherein during spraying theetching agent from the spray header, the hollow object, the sprayheader, or both are rotated.
 13. The method of claim 1, wherein thelaser system includes: an inner tube comprising the focusing lens at adistal end and a collimator at a proximal end, and an outer tubecomprising the reflector at a distal end, wherein the inner tube isnested within the outer tube with the focusing lens closest to thereflector, and wherein changing the positional relationship between thereflector and the focusing lens is moving the distal end of the innertube closer to the distal end of the outer tube.
 14. The method of claim13, wherein moving the distal end of the inner tube closer to the distalend of the outer tube is actuated by a ball screw controlled by a motorthat is part of the motion control system.
 15. The method of claim 13,wherein the reflector is mounted at the distal end of the outer tube ata first angle so that the focal point of the laser system is redirectedby a second angle toward the interior surface of the hollow object. 16.The method of claim 15, wherein when the first angle is about 45degrees, the second angle is about 90 degrees.
 17. A hollow objectcomprising an etched inner surface formed by the method of claim
 1. 18.A method for machining an interior surface of a hollow object, themethod comprising: positioning a laser system within the hollow objectso that a focal point of the laser system is focused on a coatingapplied to the interior surface of the hollow object; operating thelaser system to machine a complex pattern in the coating on the interiorsurface of the hollow object; and etching or plating the interiorsurface of the hollow object in the complex pattern by anelectrochemical etching (EChE) process, wherein the EChE processcomprises exposing the interior surface of the hollow object to anelectric current in the presence of an electrolyte solution, whereinmotion of the laser system and the hollow object is controlled by amotion control system configured to: provide rotation about alongitudinal axis, translation along the longitudinal axis, or both foreither or both of the hollow object and the laser system based on thecomplex pattern, and change a positional relationship between areflector of the laser system and a focusing lens of the laser system toaccommodate a change in a distance between the reflector and theinterior surface of the hollow object so that the focal point of thelaser system remains focused on the coating applied to the interiorsurface, wherein the change in the positional relationship is based onreal-time dimensional data of the distance between the reflector and thecoating applied to the interior surface of the hollow object collectedby a position sensing device attached to the laser system, or based ondimensional data of an interior shape of the hollow object stored on aserver.
 19. The method of claim 18, wherein the laser system includes:an inner tube comprising the focusing lens at a distal end and acollimator at a proximal end, and an outer tube comprising the reflectorat a distal end, wherein the inner tube is nested within the outer tubewith the focusing lens closest to the reflector, and wherein changingthe positional relationship between the reflector and the focusing lensis moving the distal end of the inner tube closer to the distal end ofthe outer tube by actuation of a ball screw controlled by a motor thatis part of the motion control system.
 20. A method for forming a complexpattern on an interior surface of a hollow object having a smallopening, the method comprising: passing a laser system through the smallopening of the hollow object so that a focal point of the laser systemis focused on the interior surface of the hollow object, wherein thelaser system comprises a reflector to angle the focal point with respectto a longitudinal axis of the laser system onto the interior surface ofthe hollow object; providing rotational movement, translationalmovement, or both along the longitudinal axis for one or both of thehollow object and the laser system based on the complex pattern;operating the laser system to form the complex pattern on the interiorsurface of the hollow object; and changing a longitudinal distancebetween the reflector of the laser system and a focusing lens of thelaser system to accommodate a change in a lateral distance between thereflector and the interior surface of the hollow object so that thefocal point remains focused on the interior surface, wherein the changein the distance between the reflector and the interior surface is causedby a non-uniform shape of the interior surface of the hollow object,wherein a diameter of the small opening of the hollow object is lessthan an interior diameter of the hollow object.